A stator or a stand for an electric motor typically consists of a stator packet, among other things. The stator packet is formed from individual sheet metal rings. For this purpose, the stator packet has a number of stator poles or webs, which extend radially into the interior of the stator. Between the individual stator poles there are gaps in the form of pole or winding grooves.
The inner surface of the stator, the stator poles (webs) and the pole grooves are usually overmolded or sheathed with a plastic. Alternatively, the pole grooves can also be insulated with paper. The plastic can, for example, be polymers, such as e.g. Duroplast or a thermoplastic. The plastic overmolding thereby forms the actual winding supports around each individual stator pole, which serve to accommodate the stator coils.
A stator of this type is known from the EP Patent Specification 2 015 426. This document pertaining to the state of the art discloses a stator for a drive device of a hand tool, such as a cordless screwdriver. In this case, the stator exhibits two axial stator ends, on each of which a connecting element, such as an end shield or a cap, is disposed. In its interior the stator further has multiple radially inward extending webs, which extend across the entire length of the stator and are separated by winding grooves. A stator winding, i.e. a stator coil, is attached around the webs. A groove insulation is provided between the webs and the stator winding.
The high wire tension necessary for the winding of the stator coils, can lead to a deformation of the winding supports on the ends of the stator packet. The high wire tension can also cause the winding supports to break.
In order to meet the requirements of the winding process, in particular the requirements of high wire tension, only thermoplastic materials with a high modulus of elasticity (E modulus) are currently used to manufacture the winding supports. When using thermoplastic materials, however, there may be relatively severe deformation of the winding support due to the high wire tension of the winding. Although higher filled plastics exhibit higher rigidity for use as winding supports, under the load of the wire tension, fractures in the winding supports eventually occur with these materials as well.
In addition, the heat conductivity of the materials commonly used for the winding supports poses a problem. To counteract overheating within the stator packet, the heat generated in the stator coils by the alternating current (induction heating) must, for example, be conducted over the winding supports to the outer surface of the stator packet. Plastics with optimized heat conductivity often do not satisfy the requirements of the winding process, because they too are deformed by the high wire tension or even break. The more or less only available thermoplastic materials with an optimized heat conductivity also exhibit limitations in terms of flow distance and the dependent (requisite) minimum wall thicknesses. Larger wall thicknesses are often implemented in the winding supports to counteract these limitations, which in turn, however, results in poor heat dissipation from the stator coils over the thermoplastic to the stator packet.